This invention relates to a suspension control apparatus for an automotive vehicle, and more particularly, it relates to a suspension control apparatus which can suppress rolling, nosediving, and vertical motions of a vehicle so as to provide a more comfortable ride.
During the operation of an automotive vehicle, the vehicle is subjected to accelerations in various directions due to braking, turning, changes in speed, and irregularities in the road surface which cause the vehicle body to undergo rolling, pitching, and heaving motions. These motions impart an unpleasant sensation to the passengers of the vehicle. Accordingly, in recent years, there have been proposals for suspension systems which can suppress these motions and provide a more comfortable ride.
Japanese Published Unexamined Utility Model Application No. 61-163710 and Japanese Published Unexamined Patent Application No. 62-34808 disclose suspension devices in which a fluid spring chamber such as an air spring chamber is disposed between the wheels and the body of a vehicle. By controlling the supply of compressed air to the fluid spring chambers, rolling of the vehicle body can be suppressed. For example, during turning, the suspension units on the opposite side of the vehicle from the direction of turning normally attempt to contract, while the suspension units on the same side as the direction of turning attempt to expand, resulting in rolling motion. In order to suppress this motion, a set amount of compressed air is supplied to the fluid spring chambers of the suspension units which tend to contract, and a set amount of compressed air is discharged from the fluid spring chambers of the suspension units which tend to expand. As a result, the vehicle body is tilted back from the direction of tilting caused by the turn, and the vehicle body is maintained horizontal.
Many other systems have been proposed for suppressing vehicle motions, such as systems which vary the damping force of suspension units and systems which control the action of stabilizers.
In systems which suppress rolling motions by adjusting the supply of compressed air to suspension units, the supply of air is controlled in accordance with the lateral accelerations of the vehicle as sensed by an acceleration sensor. It is therefore important that the acceleration sensor be accurately calibrated. However, the neutral point of the output of an acceleration sensor (the output corresponding to no acceleration) can vary from its initial value over long periods of time, and if this drift is not compensated for, roll suppression can not be accurately performed.